Whether to treat degenerative disease, traumatic injury, or defect, congenital or otherwise, surgical reconstructions of bony elements are common procedures in current medical practice. Regardless of anatomical region or the specifics of the reconstructive procedure, many surgeons employ orthopedic devices or implants to adjust, align and maintain the spatial relationships of adjacent bones or bony fragments during postoperative osteosynthesis. With respect to surgical reconstruction in the spinal region, it is known to employ orthopedic plates to adjust, align and maintain the spatial relationship of adjacent vertebral bodies to promote postoperative fusion. It is further known to attach the orthopedic plate to the vertebral bodies using orthopedic anchors which act to share the load and support the bone and orthopedic plate as fusion progresses.
In some cases, subsidence occurs in the bone or bone fragments to which the orthopedic plate and anchors are attached. The definition of subsidence in terms of spinal biomechanics is the sinking of the orthopedic plate and anchors having a higher elasticity modulus in one or more vertebral bodies characterized by a lower elasticity modulus, resulting in changes of the spinal geometry. Any excessive subsidence decreases the interbody space and produces both local and general kyphotization of the spine which can cause destabilization of the screw-plate and/or screw-bone interfaces (e.g. pulling-out, altered angulation or breakage of the screws).
In addition, notwithstanding the forces resulting from subsidence, over time, it has also been found that as a result of the forces placed upon the orthopedic device and anchors resulting from the movement of the spine, the orthopedic anchors can begin to back out from their installed position eventually resulting in the anchors disconnecting from the device.
As such, there exists a need for an orthopedic plate and anchors that can accommodate subsidence in the vertebral bodies as well as prevent the fasteners from “backing out” of their installed position.